The term "Jacquard mechanism" is used to describe a system of mechanical decoding developed in the 1800's by Monsieur Jacquard. This type of mechanical decoding has been and still is, used extensively in the textile industry to control various machines such as weaving machines and embroidery machines.
The principle of operation of the Jacquard mechanism is as follows. The weaving or embroidery pattern (as the case may be) is encoded on a Jacquard card as a series of holes at predetermined locations (a Jacquard card is a giant paper tape made from cardboard). The hole locations are arranged in rows and columns across the card. This card is then interrogated by the Jacquard mechanism to determine the code and to operate the machine in accordance with the code detected. The interrogation is carried out by presenting a line of mechanical pins (needles or feelers) to a row of hole locations on the card. If the pins pass through the card, a "hole" is detected and if the pins do not pass through the card, a "no hole" is detected. The particular combination of "holes" and "no holes" determines the action taken by the machine during that machine cycle. After interrogation, the pins are withdrawn and the card is progressed one row and interrogated again to determine the code for the next step (or machine cycle) and so forth. For a further discussion on how a Jacquard mechanism or Dobby machine operates, the reader is directed to the following books:
"Embroidery Schiffli and Multihead" by Coleman Schneider; and PA0 "An Introduction to Textile Mechanisms" by P. Grosberg 1986 (Ernest Benn Limited, London).
As will be appreciated, when a programme is repeated many times, the Jacquard card becomes worn by the interrogation of the Jacquard pins and a hole may appear where a "no hole" should be, creating a flaw in the pattern. At this stage, a new card is required to be punched to replace the worn out card. The Jacquard card has further disadvantages in that its sheer physical size creates storage problems as well as requiring special punching machines to produce replacement cards as they wear out. There are many machines in existence using a form of a Jacquard mechanism and industry has been looking at ways of increasing the speed of operation of these machines. Unfortunately, one of the factors limiting the speed of these machines is the speed at which the Jacquard card can be progressed to the next step for code reading and by the time required in loading and unloading the Jacquard card.
As can be seen, it is desirable to produce a device which can be used in place of the Jacquard card, to emulate the card and actuate the Jacquard mechanism in the same way as the Jacquard card. In the past, devices have been constructed to emulate the Jacquard cards so that down time is reduced and higher operating speeds may be attained. However, these devices also have had problems.
Solenoid emulators have been produced in which the "hole" or "no hole" in the paper tape is emulated by a plunger controlled by the solenoid to open or close a hole formed in a metal block which is presented to the Jacquard pins, the solenoids being controlled by electronic means to emulate the programme on a Jacquard card.
The solenoids, however, have a limited life cycle and in one programme, may operate many hundreds of times thus creating reliability problems through failure of a solenoid to operate which may not be noticed immediately resulting in a flaw in the final pattern produced. Also, the number of solenoids required make the detection of the failed solenoid difficult. When solenoids are nearing the end of their useful life, they tend to fail at a seemingly random occurrence.
A drum controller was proposed to emulate the paper tape. In this arrangement, the paper tape was replaced by a mechanism having a series of drums, each drum being independently rotatable and being rotated by respective stepper motors via gearing. The drums had holes therein to emulate the holes in the paper tape. The stepper motors were controlled electronically to rotate the drums to the required position having the same hole pattern as that part of the paper tape which was being emulated at that particular point in time. However, this proved to be unsatisfactory due to the closeness of the Jacquard pins, requiring the drums to be physically located very close together, and acceptable machining tolerances resulting in the drums rubbing on each other causing friction losses. Thus, the load on the drive motors was increased and their operational life, effectiveness and reliability was reduced. The relatively large inertia of the drums presented a speed limitation on the control of the drums both at the starting and stopping of the rotation of the drum. The allowable size of the motors was small due to the limited space available in the compact design of the device. Therefore, while the drum controller did overcome most of the disadvantages of the paper tape, it still had some disadvantages.